(1) Field of the Invention
The present invention relates to organic electroluminescent display devices (hereafter also referred to as organic EL display devices), and particularly relates to an organic EL display device including a light-adjusting layer for adjusting chromaticity of the light emitted from a light-emitting layer.
(2) Description of the Related Art
An organic EL display device is a light-emitting display device utilizing electroluminescence of organic compound, and bright light-emission at high luminance is easily obtained. Taking advantage of this property, the organic EL display device has been in practical use as a small display device used for mobile phones, for example.
The organic EL display device includes organic EL elements arranged on a substrate, and each of the organic EL display elements can be individually controlled for light emission for each pixel. The organic EL display device capable of emitting light in multiple colors includes single-color light-emitting organic EL elements each emits light in different colors (different wavelengths) such as blue, green, or red arranged periodically.
Requirements for the display quality of color display devices including multicolor light-emitting organic EL display device (hereafter also referred to as a color organic EL display device) includes high chromatic purity of outgoing light and that images with high contrast can be displayed. Conventionally, various display devices have been developed to accommodate these needs.
Here, high chromatic purity means that in chromaticity coordinate, a larger part of the region surrounded by a trajectory of single-wavelength light in a visible light range can be represented.
Contrast is a ratio of luminance in a non-light emitting region and a light-emitting region (luminance of light-emitting region divided by luminance of non-light emitting region). When the luminance of the non-light emitting region is high due to reflected external light or others, the contrast is inherently low, and the display device cannot display a sharp image. On the other hand, when the luminance of the non-light emitting region is low, the contrast is high, and deeper black can be displayed, allowing the display device to display a sharp image.
Contrast is important when watching the display device in a bright place. Since the non-light emitting region reflects external light such as interior lighting, the luminance in the non-light emitting region is high, making it difficult to increase the contrast. In order to increase the contrast in bright place, it is necessary to decrease the reflectance of the external light at the non-light emitting region.
In view of these concerns, in a display device including only light-emitting pixels, the function for increasing the chromatic purity and suppressing reflection of external light is not sufficient.
The patent literature 1 (Japanese Unexamined Patent Application Publication No. 2003-173875) discloses a multicolor light-emitting organic EL display device with a wavelength selectivity that allows a portion of a wavelength selecting layer (color filter) corresponding to each organic EL element to selectively transmit light in blue, green, or red emitted from the organic EL element. A conventional configuration for providing visible light absorbing material on the non-light emitting region between adjacent organic EL elements (referred to as black matrix) may be combined with this configuration.
According to this multicolor organic EL display device, a color filter with a wavelength selecting property suitable for the color of outgoing light increases the chromatic purity of outgoing light from each organic EL element, and the visible-light absorbing material absorbing the external light allows a display of an image with high contrast.
The patent literature 2 (Japanese Unexamined Patent Application Publication No. 2007-226239) discloses a display filter which absorbs light at a wavelength between the wavelengths of two outgoing light (for example, an intermediate wavelength between blue and green and an intermediate wavelength between green and red) at the entire surface and a plasma display panel using the display filter. With this display filter, the chromatic purity of the outgoing light increases by an absorption of the light at the intermediate wavelength included in the outgoing light from each light-emitting pixel.